Partially crosslinked polymer used in correcting subterranean formation permeability

Abstract

A method is provided for obtaining good residual resistance factor at relatively low ratios of crosslinking agents to polymer for plugging fractured or porous media using a method of injecting into the formation a first aqueous polymer solution followed by an injection of crosslinking agents capable of gelling the polymer solution and thereafter injecting a second aqueous polymer solution that is capable of being gelled by the crosslinking agents. In each of the aqueous polymer solutions the polymer is already partially crosslinked before the polymer solution is injected into the formation. This process is applicable to production wells and injection wells.

I claim: 
     
       1. A method for treating a subterranean formation which is penetrated by at least one well bore, comprising: a. injecting into the formation through a well bore a first aqueous solution of partially crosslinked polymer;   b. thereafter injecting a complexing ionic solution of multivalent cations and retarding ion; and   c. thereafter injecting into the formation through the well bore a second aqueous solution of partially crosslinked polymer.   
     
     
       2. A method according to claim 1 wherein said treating is carried out through a producing well penetrating said formation. 
     
     
       3. A method according to claim 1 for improving the water injection profile of wells used in water flooding, polymer flooding, surfactant flooding, and miscible flooding. 
     
     
       4. A method according to claim 3 wherein the polymer is comprised of a partially hydrolyzed polyacrylamide. 
     
     
       5. A method according to claim 1 wherein said first and second aqueous solutions of partially crosslinked polymer comprise a mixture of aqueous polymer solution and an amount of complexing ionic solution of multivalent cations and retarding ions sufficient to partially crosslink said polymer. 
     
     
       6. A method according to claim 5 wherein the complexing ionic solution is aluminum citrate. 
     
     
       7. A method according to claim 1 wherein the first and second aqueous polymer solutions are comprised of from about 200 to about 10,000 ppm of a partially crosslinked polymer selected from the group consisting of polyacrylamides, polyacrylonitrile, partially hydrolyzed polyacrylonitriles, partially hydrolyzed polyacrylamides, polyacrylic acid, polyvinylpyrrolidone, polysaccharides, carboxymethylcellulose, other substituted celluloses, polyvinyl alcohol, polystyrene sulfonates, copolymers of acrylonitrile with acrylic acid or 2-acrylamido-2-methyl-1-propane sulfonic acid; and a complexing ionic solution which is comprised of from about 25 to about 10,000 ppm of multivalent cations selected from the group consisting of Fe 2   + , Fe 3   + , Al.sup. 3 + , Ti 4   + , Zn 2   + , Sn 4   + , Ca 2   + , Mg 2   + , and Cr 3   + , and from about 25 to about 10,000 ppm of retarding anions selected from the group consisting of acetate, nitrilotriacetate, tartrate, citrate, tripolyphosphate, metaphosphate, gluconate, and orthophosphate. 
     
     
       8. A method according to claim 7 wherein said polymer solution contains an amount of crosslinking agent in the range of about 0.01 to about 5 grams of complexing metal per gram of polymer. 
     
     
       9. A method according to claim 1 wherein the first and second polymer solutions are comprised of the same polymer.